Question

The following codeigniter function takes a (string) parameter and returns the (integer) ID of the row. It works fine if i pass string values, but if integer 0 is passed, it returns ID of first row in database. In principle, it should return the user_id only if the the user_name exists in the database. Since there is no user_name called 0, it should return false.
Can someone tell why it is behaving like this and how it can be fixed?

Thanks.

public function get_user_id($user_name)
    {
        $this -> db -> select('user_id');
        $this -> db -> from('users');
        $this -> db -> where('user_name', $user_name);
        $this -> db -> limit(1); 

        $query = $this->db->get();

        if ( $query->num_rows > 0 )
        {
            $row = $query->row();
            return $row->user_id;
        }       
    return false;       
    }

For example:

$user_name = "test";  //works fine, returns id.
$user_name = "0";   //works fine, doesnt return anything
$user_name = 0;     //Problem. returns ID of first row.

Answer 1

You should add a test of the kind if ($user_name == "") return false; to catch this.

Apparently where with second argument 0 always matches, e.g. translates into SQL WHERE user_name, rather than WHERE user_name = "", and WHERE user_name is short-hand for WHERE user_name != "" — the opposite of what you wanted 🙂

Running this test at the beginning saves you a full database query when you’re passed an argument that will necessarily result in false.